In the practice of dentistry, it is important to have the necessary dental instruments held in a convenient and accessible location. To facilitate easy access to the instruments, it is desireable to have the instrument holder attached to the dental chair backrest in such a way that the holder maintains a desired orientation even though the dental chair backrest may be moved.
Various mechanism have been designed to attach instrument holders to a dental chair. U.S. Pat. No. 4,883,316 to Austin, Jr., et al., herein incorporated by reference, discloses a mechanism having the capability of maintaining an instrument holder in a desired orientation irrespective of movement of the dental chair backrest. That patent describes an instrument holder that is mounted to the backrest by an attachment member that can pivot relative to the backrest. The attachment member is normally held stationary by a cable that extends from the attachment member to the chair seat. The instruments hang generally vertically from the instrument holder. When the chair backrest is tilted from an upright position, the cable tightens to pivot the attachment member so that the instrument holder maintains the orientation for hanging the instruments vertically. A spring is connected to the attachment member and is stretched when the backrest is tilted. When the backrest is moved back toward the upright position, the cable loosens and the stretched spring pulls the attachment member so it pivots back toward its original position, thereby maintaining the instrument holder in the same orientation mentioned above.
The above mentioned spring also serves as a safety mechanism. In this regard, whenever the instrument holder encounters a solid object as the backrest is moved from the upright position, the attachment member is free to rotate against the tension in the spring so that the downward motion of the instrument holder is effectively stopped, thereby preventing damage to the instrument holder.
A second spring is provided for anchoring the cable to the chair seat in a manner such that the second spring will compress in the event the instrument holder encounters a solid object as the chair moves toward the upright position. Accordingly, the second spring prevents damage to the instrument holder by effectively stopping the upward motion of the instrument holder.
The cable and spring mechanism just described also includes adjustment mechanisms for increasing the tension in the cable after the cable becomes stretched due to repeated use.